An energy transmission system for exchanging thermal energy of a medium in a sealed loop with a compressor, a control valve, and two heat exchangers between the compressor and the control valve such that a medium flowing between the compressor and the control valve absorbs thermal energy from one heat exchanger and releases thermal energy through the other heat exchanger. The compressor (22) changes the pressure of the medium in the loop such that the pressure through one heat exchanger is different from the pressure through the other heat exchanger, and the physical state of the medium is different between regions of the sealed loop.